The purpose of the proposed project is to elucidate the molecular regulatory mechanisms underlying initiation of fungal development. I will study these processes in the genetically well characterized filamentous ascomycete, Aspergillus nidulans. My previous work helped to define a pathway comprised of three regulatory genes, brlA, abaA, and wetA, that controls the temporal and spatial expression of other developmentally regulated genes. The experiments described here ar aimed at understanding the events leading up to activation of the first gene in the pathway, brlA. Five projects with interrelated goals are proposed. They are: 1) To identify cis-acting regulatory regions responsible for developmental control of brlA and to characterize interactions between these sequence elements and DNA binding proteins in crude extracts; 2) To isolate genes encoding transacting brlA regulatory proteins based on their in vitro binding activities when expressed in E. coli or their in vivo regulatory activity when expressed in either A. nidulans or S. cerevisiae; 3) To conduct mutational searches to identify genes directly involved in brlA control; 4) To isolate and characterize six genetic loci with properties indicating that their products are required for specific aspects of developmental induction; and 5) To isolate genes encoding mRNAs that are induced prior to brlA during conidiophore development and to examine the effects of developmental mutants on their expression. This work will contribute to our understanding of the reproductive molecular biology of a group of organisms that includes animal and plant pathogens as well as medically and industrially important species. The results could provide novel approaches for controlling both the positive and negative activities of fungi. They may also provide basic information regarding the broad question of how eukaryotic cells become responsive to specific stimuli that activate appropriate developmental pathways.